Air injection into a mature waterflooded light oil reservoir. Laboratory and simulation results for Barrancas Field, Argentina

Abstract

ABSTRACT This paper describes preparations for an air injection pilot into a mature waterflooded light oil reservoir in Barrancas field, Argentina. Primary development started in 1954, with waterflooding beginning in 1967.As the reservoir characteristics are quite similar to economically viable air injection projects in the Williston Basin, the feasibility of air injection for Barrancas was investigated. The upper layer has contributed 40 % of the total field production with 46 % of the injected water entering into the sequence. The three lower zones appear to be good candidates for air injection due to their current high oil saturation. Laboratory studies carried out at the University of Calgary were aimed at determining pilot design information (self-ignition, fuel availability, air requirements). These included accelerated rate calorimetry, ramped test oxidation, and high pressure/high temperature combustion tube tests. The combustion tube showed excellent burning characteristics (temperature profiles >300 °C). A reasonable simulation match was obtained using compositional PVT from Barrancas to define the component description. The laboratory simulations were then used to explore various additional sensitivities. The history match model consisted of a target pilot zone of six inner producers surrounded by additional outer producers and numerous water injectors. The four sequences were separated with transmissibility barriers of varying strength, and also contained channels with permeability enhancements. The magnitudes of these factors and the water-oil relative permeability characteristics were adjusted during the history match. The black oil reservoir description was then converted to the thermal/compositional representation for the air injection sensitivity runs. Several air injection scenarios with two air injectors were considered, including variation in air injection rates and injection completion zones, and wet combustion as a follow-up to dry. According to the results of this study, the process is technically feasible. Currently the economic aspects are being studied before pilot implementation. INTRODUCTION The studies described in this paper result from the search for EOR processes that can be applied in light oil mature fields previously developed by primary and secondary recovery. As a result of a first screening, it was found that air or gas injection was likely to be carried out in most fields. Later geologic and reservoir characteristics of the available candidate fields were analyzed. The Barrancas Field emerged as a natural candidate due to two reasons:The feasibility of injecting gas was determined some years ago.There are several successful projects being applied in deep and hot light oil reservoirs[1,2,3,4]withcharacteristics similars to those of Barrancas field. The available bibliography reported a process named COFCAW[5] (Combination of Forward Combustion and Waterflooding), carried out in the sixties. One of the main conclusions of this project which started as an inverted five-spot pilot and then extended to 9 patterns, was that the oil price was a determining factor in the project economy. Current high oil prices will impact favourably on the economics of the EOR process visualized for the Barrancas Field.